4x^2-17x-15=0 solve quadratic formula

Question

I know the answer is  5, -3/4 but I am missing something. please help show each step and use quadratic formula. thank you

Answer 1

{17 + √[(-17)²-(4)(4)(-15)]}/ (2*4) = 40/8 = 5

 

1. square -17 = 289

2. multiply 4, 4, and -15 to get -240
3. subtract -240 from 289 = 289--240= 289+240= 529
4. take the square root of 529 = √529= 23
5. add 23 to 17 = 23+17=40
6. multiply 2 by 4 = 2*4 = 8
7. Divide 40 by 8 = 40/8 =5

AND

{17 - √[(-17)²-(4)(4)(-15)]}/ (2*4) = -6/8 = -3/4

 

1. square -17 = 289
2. multiply 4, 4, and -15 to get -240
3. subtract -240 from 289 = 289--240= 289+240= 529
4. take the square root of 529 = √529= 23
5. subtract 23 from 17 = 17-23=-6
6. multiply 2 by 4 = 2*4 = 8
7. Divide -6 by 8 = -6/8 = -3/4

 

I hope this helps.