15 a .(2-3√2)²=4-2*2*3√2+9*2=4-12√2+18=22-12√2=2(11-6√2)
15 b (2√3-3√6)²=4*3-2*2*3√18+9*6=12-12√18+54=66-12*3√2=66-36√2=6(11-6√2)
16 a 7²-(4√3)²=49-16*3=49-48=1
16 b (5√3)²-(2√5)²=25*3-4*5=75-20=55
17a (x²-4)(x²+4)-(x⁴+2x²+1)+2(x²+2x+1)=x⁴-16-x⁴-2x²-1+2x²+4x+2=4x-15
17b x³-3x+4x²-12-x(x²+4x+4)+(x²-2x+1)=x³-3x+4x²-12-x³-4x²-4x+x²-2x+1=x²-9x-11
