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x1 + x2 = -b/a = -(-2)/1 = 2
x1 x2 = c/a = 4/1 = 4
maka pers kuadrat baru yg akar-akarnya :
a) x1² + x2 dan x1 + x2²
misal p = x1² + x2 dan q = x1 + x2², maka
p + q = x1² + x2 + x1 + x2² = (x1²+x2²) + x1+x2 =
(x1+x2)² - 2x1x2 + x1 + x2 = (2)² - 2(4) + 2 = 4 - 8 + 2 = -2
dan pq = (x1²+x2)(x2²+x1) = (x1x2)² + x1³ + x2³ + x1x2 =
(x1x2)²+(x1+x2)³-3x1x2(x1+x2)+x1x2 = 4²+2³-3(4)(2)+4 = 4
jadi PKB-nya : x² - (p+q)x + pq = 0
x² - (-2)x + 4 = 0
x² + 2x + 4 = 0