Question

Find the roots x2-2x-15=0 by quadratic formula

Answer 1

By quadratic formula

-b +-√b²- 4 ac / 2 a

= a = 1 , b = - 2 c = -15

= - ( - 2 ) + √ (-2 ) ² - 4*1 *-15 / 2*1

= 2+ √ 4+60 /2

= 2+ √ 64 /2

= 2+ - 8 /2

For positive --- 2+8 /2

10/2 = 5

For negative ---- 2-8 /2

-6/2 = -3

Hope it's help you.

Answer 2

Answer:

${x}^{2} - 2x - 15 = 0 \\ {x}^{2} + 3x - 5x - 15 = 0 \\ x(x + 3) - 5(x + 3) = 0 \\ (x + 3)(x - 5) = 0 \\ x + 3 = 0 \: \: \: or \: \: \: x - 5 = 0 \\ \large{\boxed{ \boxed{x = { \underline{ \underline{ - 3}}} \: \: \: or \: \: \: x= { \underline{ \underline{5}}}}}}$