Tìm x, biết: a) x^2 -25 = 3x -15 b) (x-1)^3 +3(x+1)^2 = (x^2 -2x
Giải thích
a)
x2–25=3x–15x2–25−3x–15=0x−5x+5−3x−5=0x−5x+5−3=0x−5x+2=0⇒x−5=0x+2=0⇒x=5x=−2
Vậy x∈−2; 5
b)
x–13+3x+12=x2–2x+4x+2x3−3x2+3x−1+3x2+2x+1=x3+8x3−3x2+3x−1+3x2+6x+3=x3+89x+2=89x=6x=23
Vậy x=23