SOLUTION: I left my notes at school. I don't know how to solve this problem (3x+5)(7x-15)=180

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Question 1030479: I left my notes at school. I don't know how to solve this problem
(3x+5)(7x-15)=180
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
(3x+5)(7x-15)=180
3x(7x-15)+5(7x-15)=180
21x%5E2+-45x%2B35x-75=180

21x^2-10x-255=0
Find the roots of the equation by quadratic formula

a= 21 b= -10 c= -255

b^2-4ac= 100 - -21420
b^2-4ac= 21520 sqrt%28%0921520%09%29= 146.7
x=%28-b%2B-sqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=%28-b%2Bsqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=( 10 + 146.7 )/ 42
x1= 3.73
x2=( 10 -146.7 ) / 42
x2= -3.25

x = 3.73 or -3.25