Question

Salah satu akar persamaan kuadrat x^2-4x-(2m+5)=0 adalah 7. akar yang lainnya adalah ....

Answer 1

Diket :
a = 1
b = -4
c = -2m-5
x1 = 7

ditanya : x2....?
jawab :

x1 + x2 = -b/a
7 + x2 = -(-4)/1
7 + x2 = 4
x2 = 4-7
x2 = -3

x1 = 7
• x1 -7 = 0

x2 = -3
x2 +3 = 0

• (x-7)(x+3) = 0
• x^2 +3x-7x-21 = 0
• x^2 -4x -21= 0

nilai m =
• -(2m+5) = -21
• 2m+5 = 21
• 2m = 21-5
• 2m = 16
• m = 16/2 = 8

Answer 2

(x-7)(x+m) = x²-4x-2m-5
x²+mx-7x-7m = x²-4x-2m-5
4x-7x+2m-7m+mx = -5
-3x-5m+mx = -5
-21-5m+7m = -5
-21+2m = -5
2m = 16
m = 8