Question

Carilah akar tiap persamaan berikut dengan menggunakan kuadrat sempurna!
1. X2 - 10x + 21 = 0
2. X2 - 18x + 32 = 0

Answer 1

1) X2-10X+21=0
    (X-7)(X-3)
X=7 atau X=3
2) X2-18X+32=0
    (X-16)(X-2)
X=16 atau X=2

Answer 2

1. x^2 - 10x + 21= 0
x^2 - 10x = -21 (ruas kanan konstanta)
kedua ruas ditambah (1/2 koefisien x)^2 yaitu (1/2 . 10)^2 = (5)^2
x^2-10x+(5)^2 = -21 + (5)^2
(x+5)^2 = -21 + 25
9x+5)^2 = 4
x+5 = akar 4
x+5 = plus minus 2
x= -5 plus minus 2
x! = -5 +2 = -3
x2+ -5 -2 = -7
2. x2-18x+32= 0
x2-18x= -32
(1/2 . -18)^2 = (-9)^2
x^2 -18x + (-9)^2 = -32 + (-9)^2
(x-9)^2 = -32 + 81
(x-9)^2 = 49
x-9 = akar 49
x-9 = plus minus 7
x= 9 plus minus 7
jdi
x1 = 9+7 =16
x2 = 9-7 =2