Giải câu 2 trang 57 sách toán VNEN lớp 9 tập 2.
a) 4xx+2=x+1x−2 (ĐK: x≠±2)
⇔4x(x−2)−(x+1)(x+2)=0
⇔4x2−8x−x2−3x−2=0
⇔3x2−11x−2=0
Δ=(−11)2−4×3×(−2)=145
⇒x1=11+1456(tmdk);x2=11−1456 (tmđk)
b) 2x−1x+3=x+32x−1 (ĐK: x≠0;x≠12)
⇔(2x−1)2+3x(2x−1)−(x+3)x=0
⇔9x2−10x+1=0 (2)
Phương trình (2) có a+b+c=0
⇒x1=1(tmdk);x2=19(tmdk)
c) x−2x+xx−1−116=0 (ĐK: x≠0;x≠1)
⇔6(x−2)(x−1)+6x2−11x(x−1)=0
⇔x2−7x+12=0 (3)
Δ=(−7)2−4×1×12=1
⇒x1=4(tmdk);x2=3(tmdk)
d) 2xx−2−5x−3=5x2−5x+6 (ĐK: x≠2;3
⇔2x(x−3)−5(x−2)−5=0
⇔2x2−11x+5=0
Δ=(−11)2−4×2×5=81⇒Δ=9
⇒x1=5(tmdk);x2=12(tmdk)
e) 13x2−27+34=1+1x−3 (ĐK: x≠±3)
⇔4+3(3x2−27)−4(3x2−27)−12(x+3)=0
⇔4+9x2−81−12x2+108−12x−36=0
⇔3x2+12x+5=0
Δ′=62−3×5=21
⇒x1=−6+213(tmdk);x2=−6−213