(a-1)/(√a-∛a)=(∛a-1)(∛a²+∛a*1+1³)/(∛a(∛a-1))=(∛a²+∛a+1)/∛a=∛a²*(∛a²+∛a+1)/a.
1)(3x-2)(3x+2)-(2x-3)²=3x(x+7)-17
9x²-4-(4x²-12x+9)=3x²+21x-17
9x²-4-4x²+12x-9-3x²-21x+17=0
2x²-9x+4=0
D=(-9)²-4*2*4=81-32=49=7²
x1=(9-7)/(2*2)=2/4=0,5
x2=(9+7)/(2*2)=16/4=4
Ответ:x1=0,5;x2=4
2)3x(5x+3)=2x(6x+5)+2
15x²+9x=12x²+10x+2
15x²+9x-12x²-10x-2=0
3x²-x-2=0
D=(-1)²-4*3(-2)=1-(-24)=1+24=25=5²
x1=(1-5)/(2*3)=-4/6=-2/3
x2=(1+5)/(2*3)=6/6=1
Ответ:x1=-2/3;x2=1
A4=a1+3d=-3+3*7=-3+21=18
S4=(a1+a4)*4/2 = (a1+a4)*2=15*2=30