SOLUTION: Please help me solve this: 15x^2-7x-4=0

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Question 195565: Please help me solve this: 15x^2-7x-4=0
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
15x%5E2-7x-4=0 Start with the given equation.


Notice we have a quadratic equation in the form of ax%5E2%2Bbx%2Bc where a=15, b=-7, and c=-4


Let's use the quadratic formula to solve for x


x+=+%28-b+%2B-+sqrt%28+b%5E2-4ac+%29%29%2F%282a%29 Start with the quadratic formula


x+=+%28-%28-7%29+%2B-+sqrt%28+%28-7%29%5E2-4%2815%29%28-4%29+%29%29%2F%282%2815%29%29 Plug in a=15, b=-7, and c=-4


x+=+%287+%2B-+sqrt%28+%28-7%29%5E2-4%2815%29%28-4%29+%29%29%2F%282%2815%29%29 Negate -7 to get 7.


x+=+%287+%2B-+sqrt%28+49-4%2815%29%28-4%29+%29%29%2F%282%2815%29%29 Square -7 to get 49.


x+=+%287+%2B-+sqrt%28+49--240+%29%29%2F%282%2815%29%29 Multiply 4%2815%29%28-4%29 to get -240


x+=+%287+%2B-+sqrt%28+49%2B240+%29%29%2F%282%2815%29%29 Rewrite sqrt%2849--240%29 as sqrt%2849%2B240%29


x+=+%287+%2B-+sqrt%28+289+%29%29%2F%282%2815%29%29 Add 49 to 240 to get 289


x+=+%287+%2B-+sqrt%28+289+%29%29%2F%2830%29 Multiply 2 and 15 to get 30.


x+=+%287+%2B-+17%29%2F%2830%29 Take the square root of 289 to get 17.


x+=+%287+%2B+17%29%2F%2830%29 or x+=+%287+-+17%29%2F%2830%29 Break up the expression.


x+=+%2824%29%2F%2830%29 or x+=++%28-10%29%2F%2830%29 Combine like terms.


x+=+4%2F5 or x+=+-1%2F3 Simplify.


So the answers are x+=+4%2F5 or x+=+-1%2F3