(1-2x)^5=1-5(2x)+10(2x)²-10(2x)³+5(2x)^4-(2x)^5=1-10x+40x²-80x³+80x^4-32x^5
（1-2x）^5＝1-5×2x+10×4x²-10×8x³+5×16x^4-32x^5＝1-10x+40x²-80x³+80x^4-32x^5
