Solve: (x-1)(x+1)(x-2) = -2x²-x³ | Comparing Factored and Expanded Forms

Question

(x1)(x+1)(x2)=2x2x3 (x-1)(x+1)(x-2)=-2x^2-x^3

Video Solution

Solution Steps

00:00 Solve
00:03 Let's use shortened multiplication formulas to open the parentheses
00:15 Open parentheses properly
00:18 Each term multiplies each term
00:38 Collect terms and reduce what's possible
00:46 Isolate X
00:50 And this is the solution to the question

Step-by-Step Solution

Let's solve the equation by simplifying the expression on the left side in two steps. First, we'll multiply the expressions in the two leftmost pairs of parentheses:

We'll use the shortened multiplication formula for squaring a binomial:

(a±b)2=a2±2ab+b2 (a\pm b)^2=a^2\pm2ab+b^2

Since these two pairs of parentheses are being multiplied by another expression (which is also in parentheses), we'll put the result in parentheses (marked with an underline later):

(x1)(x+1)(x2)=2x2+x3(x212)(x2)=2x2+x3(x21)(x2)=2x2+x3 \underline{ (x-1)(x+1)}(x-2)=-2x^2+x^3 \\ \underline{ (x^2-1^2)}(x-2)=-2x^2+x^3 \\ (x^2-1)(x-2)=-2x^2+x^3

Let's continue and simplify the expression on the left side using the expanded distribution law:

(a+b)(c+d)=ac+ad+bc+bd (a+b)(c+d)=ac+ad+bc+bd

Additionally, we'll use the law of exponents for multiplying terms with equal bases:

aman=am+n a^ma^n=a^{m+n} We'll now apply these laws and expand the parentheses in the expression in the equation:

(x21)(x2)=2x2+x3x32x2x+2=2x2+x3 (x^2-1)(x-2)=-2x^2+x^3 \\ x^3-2x^2-x+2=-2x^2+x^3 \\ We'll continue and combine like terms, by moving terms between sides. Later - we can see that the terms with squared and cubed powers cancel out, therefore it's a first-degree equation, which we'll solve by isolating the variable term on one side and dividing both sides of the equation by its coefficient:

x32x2x+2=2x2+x3x=2/:(1)x=2 x^3-2x^2-x+2=-2x^2+x^3\\ -x=-2\hspace{8pt}\text{/}:(-1)\\ \boxed{x=2}

Therefore, the correct answer is answer C.

Answer

x=2 x=2