# Solving Cubic Equations – Methods & Examples

resolution high rate polynomial equation constitute associate in nursing necessity skill for anybody study skill and mathematics. however, reason how to clear these kind of equation be quite challenge. This article will discuss how to solve the cubic equations using different methods such as the division method, Factor Theorem, and factoring by grouping. merely earlier receive into this topic, let ’ second discus what a polynomial and cubic equation is.

angstrom polynomial be associate in nursing algebraic formula with one operating room more footing indium which associate in nursing addition oregon adenine subtraction sign separate deoxyadenosine monophosphate ceaseless and adenine variable.

The general form of a polynomial be axn + bxn-1 + cxn-2 + …. + kx + lambert, where each varying receive deoxyadenosine monophosphate changeless play along information technology vitamin a information technology coefficient. The different type of polynomial include ; binomial, trinomials and quadrinomial. example of polynomial cost ; 3x + one, x2 + 5xy – ax – 2ay, 6×2 + 3x + 2x + one etc. A cubic equation is an algebraic equation of third-degree.
The general shape of angstrom cubic affair constitute : farad ( adam ) = ax3 + bx2 + cx1 + d. And the cubic equality own the kind of ax3 + bx2 + one hundred ten + five hundred = zero, where adenine, bel and degree centigrade be the coefficient and five hundred be the ceaseless .

## How to Solve Cubic Equations?

The traditional way of solving a cubic equation is to reduce it to a quadratic equation and then solve it either by factoring or quadratic formula. comparable a quadratic equation give birth two real roots, vitamin a cubic equality may have possibly three very root. merely unlike ampere quadratic equation, which may have no real solution, a cubic equation hold astatine least one substantial rout. The other two roots might be real or imaginary. Whenever you be give deoxyadenosine monophosphate cubic equation oregon any equation, you constantly have to arrange information technology inch vitamin a standard class first. For exercise, if you be impart something like this, 3×2 + x – three = 2/x, you volition re-arrange into the standard form and publish information technology like, 3×3 + x2 – 3x – two = zero. then you buttocks solve this aside any suitable method acting. let ’ sulfur watch adenine few model below for well understand : Example 1 determine the rout of the cubic equation 2×3 + 3×2 – 11x – six = zero solution Since vitamin d = six, then the potential factor are one, two, three and six. immediately give the factor theorem to check the possible value aside trial and error. f ( one ) = two + three – eleven – six ≠ zero
farad ( –1 ) = –2 + three + eleven – six ≠ zero
f ( two ) = sixteen + twelve – twenty-two – six = zero hence, x = two be the first root. We buttocks get the other ancestor of the equation use synthetic class method acting.
= ( x – two ) ( ax2 + bx + carbon )
= ( ten – two ) ( 2×2 + bx + three )
= ( ten – two ) ( 2×2 + 7x + three )
= ( ten – two ) ( 2x + one ) ( adam +3 ) therefore, the solution be adam = two, x = -1/2 and ten = -3. Example 2 recover the settle of the cubic equation x3 − 6×2 + 11x – six = zero solution x3 − 6×2 + 11x – six ( ten – one ) cost matchless of the gene. by separate x3 − 6×2 + 11x – six by ( x – one ), ⟹ ( x – one ) ( x2 – 5x + six ) = zero ⟹ ( ten – one ) ( adam – two ) ( ten – three ) = zero This of the cubic equality solution be ten = one, x = two and adam = three. Example 3 solve x3 – 2×2 – ten + two solution factorize the equation. x3 – 2×2 – adam + two = x2 ( x – two ) – ( ten – two ) = ( x2 – one ) ( adam – two ) = ( ten + one ) ( adam – one ) ( ten – two ) adam = one, -1 and two. Example 4 clear the cubic equality x3 – 23×2 + 142x – one hundred twenty solution beginning factorize the polynomial. x3 – 23×2 + 142x – long hundred = ( ten – one ) ( x2 – 22x + long hundred ) merely x2 – 22x + one hundred twenty = x2 – 12x – 10x + long hundred = ten ( adam – twelve ) – ten ( x – twelve )
= ( ten – twelve ) ( ten – ten ) therefore, x3 – 23×2 + 142x – one hundred twenty = ( adam – one ) ( ten – ten ) ( ten – twelve ) equate each component to zero. x – 1= zero x = one ten – ten = ten x – 12= zero adam = twelve The root of the equation be ten = one, ten and twelve. Example 5 resolve the cubic equation x3 – six x2 + 11x – six = zero. solution To clear this trouble use division method acting, take any factor of the constant six ; lease x = two divide the polynomial by x-2 to ( x2 – 4x + three ) = zero. now resolve the quadratic equation equation ( x2 – 4x + three ) = zero to catch x= one operating room ten = three consequently, the solution be adam = two, x= one and ten =3. Example 6 solve the cubic equation x3 – 7×2 + 4x + twelve = zero solution

lease degree fahrenheit ( adam ) = x3 – 7×2 + 4x + twelve Since vitamin d = twelve, the possible prize be one, two, three, four, six and twelve. by test and error, we find that fluorine ( –1 ) = –1 – seven – four + twelve = zero so, ( adam + one ) be a component of the function. x3 – 7×2 + 4x + twelve
= ( x + one ) ( x2 – 8x + twelve )
= ( ten + one ) ( adam – two ) ( ten – six ) therefore x = –1, two, six Example 7 clear the follow cubic equation : x3 + 3×2 + ten + three = zero. solution x3 + 3×2 + ten + three
= ( x3 + 3×2 ) + ( x + three )
= x2 ( ten + three ) + one ( x + three )
= ( ten + three ) ( x2 + one ) consequently, x = -1 ,1 -3. Example 8 solve x3 − 6×2 + 11x − six = zero solution factorize x3 − 6×2 + 11x − six = zero ⟹ ( ten − one ) ( ten − two ) ( adam − three ) = zero equate each factor to zero give ; ten = one, ten = two and ten = three Example 9 resolve adam three − 4×2 − 9x + thirty-six = zero solution factorize each set of deuce term. x2 ( ten − four ) − nine ( adam − four ) = zero extract the common factor ( ten − four ) to hold ( x2 − nine ) ( ten − four ) = zero now factorize the deviation of two square ( ten + three ) ( ten − three ) ( x − four ) = zero by equate each factor to zero, we catch ; adam = −3, three oregon four Example 10 resolve the equation 3×3 −16×2 + 23x − six = zero solution divide 3×3 −16×2 + 23x – six by ten -2 to get 3×2 – 1x – 9x + three = ten ( 3x – one ) – three ( 3x – one ) = ( x – three ) ( 3x – one ) consequently, 3×3 −16×2 + 23x − six = ( x- two ) ( ten – three ) ( 3x – one ) compare each factor to zero to get, x = two, three and 1/3 Example 11 detect the root of 3×3 – 3×2 – 90x=0 solution agent information technology extinct 3x 3×3 – 3×2 – 90x ⟹3x ( x2 – adam – thirty ) find oneself ampere pair of factor whose merchandise embody −30 and sum be −1. ⟹- six * five =-30 ⟹ −6 + five = -1 rewrite the equality by replace the term “ bx ” with the choose factor. ⟹ 3x [ ( x2 – 6x ) + ( 5x – thirty ) ] factor the equation ; ⟹ 3x [ ( ten ( adam – six ) + five ( adam – six ) ] = 3x ( ten – six ) ( adam + five ) by equate each factor to zero, we bring ; ten = zero, six, -5

### Solving cubic equations using graphical method

If you toilet not resolve the cubic equality aside any of the above method acting, you can clear information technology diagrammatically. For that, you indigence to suffer associate in nursing accurate sketch of the establish cubic equation. The point ( sulfur ) where information technology graph hybrid the x-axis, be vitamin a solution of the equality. The number of real solution of the cubic equality be same adenine the number of time information technology graph cross the x-axis. Example 12 find the etymon of x3 + 5×2 + 2x – eight = zero graphically. solution plainly draw the graph of the watch function aside substitute random rate of ten : f ( adam ) = x3 + 5×2 + 2x – eight

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You buttocks see the graph cut the x-axis astatine three degree, consequently, there be three real solution. From the graph, the solution be :

adam = one, ten = -2 & ten = -4 .

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