SOLUTION: If x^2 = 3x + 4, then x^5 is equal to: (A) 3x + 4 (B) 13x + 12 (C) 51x + 52 (D) 205x + 204 (E) 819x + 820

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: If x^2 = 3x + 4, then x^5 is equal to: (A) 3x + 4 (B) 13x + 12 (C) 51x + 52 (D) 205x + 204 (E) 819x + 820      Log On


   

Question 283359: If x^2 = 3x + 4, then x^5 is equal to:
(A) 3x + 4 (B) 13x + 12 (C) 51x + 52 (D) 205x + 204 (E) 819x + 820
Found 2 solutions by richwmiller, nabla:
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
d)205x+204
The other tutor found it one way.
I solved for x
x=-1 or 4
Then I went through the possibles answers to see which one fit.

Answer by nabla(475) About Me  (Show Source):
You can put this solution on YOUR website!
You solve this by substituting x^2 into the expansion of x^5.
x%5E2=3x%2B4
x%5E5=x%2Ax%5E2%2Ax%5E2
---> x%5E5=x%283x%2B4%29%283x%2B4%29

D is indeed the answer, but I hope you now see how to do it.