(7-2x)(49+14x4x^2)+2x(2x-5)(2x+5)=43 100(0,2x+1)(0,04x^2-0,2x+1)=5x(0,16x^2-4)

(7-2x)(49+14x+4x^2)+2x(2x-5)(2x+5)=43
343-8x³+8x³-50x=43
50x=343-43
50x=300
x=300:50
x=6

100(0,2x+1)(0,04x^2-0,2x+1)=5x(0,16x^2-4)
100(0,008x³+1)=5x(0,16x²-4)
0,8x³+100-0,8x³+20x=0
20x=-100
x=-100:20
x=-5