第一:9x^2-12x+4
=(3x)²-12x+2²
=(3x-2)²
第二:1/4a^2-3/5ab+9/ 25b^2
=(1/2a)²-3/5ab+(3/5b)²
=(1/2a-3/5b)²
第三:-x^2+1/2xy-1/16y^2
=-[x²-1/2xy+(1/4y)²]
=-(x-1/4y)²
第四4(x-y)^2+20(x-y)
=4(x-y)(x-y+5)
第一:9x^2-12x+4
=(3x)²-12x+2²
=(3x-2)²
第二:1/4a^2-3/5ab+9/ 25b^2
=(1/2a)²-3/5ab+(3/5b)²
=(1/2a-3/5b)²
第三:-x^2+1/2xy-1/16y^2
=-[x²-1/2xy+(1/4y)²]
=-(x-1/4y)²
第四4(x-y)^2+20(x-y)
=4(x-y)(x-y+5)