4x²y－8xy²＋7－4x²y＋12xy²－4
=4x^2y-4x^2y+12xy^2-8xy^2+7-4
=4xy^2+3
5xy－3x²y－7xy²＋6xy－12xy＋7xy²＋8x²y
=8x^2y-3x^2y+5xy+6xy-12xy+7xy^2-7xy^2
=5x^2y-xy
=xy(5x-1)
2a²b＋1/2a²b
=(4a^4b^2+1)/2a^2b
=(2a^2b+1)(2a^2b-1)/2a^2b
﹣a²b＋2a²b
=a^2b
a²－2ab＋b²＋2a²＋2ab－b²
=a^2+2a^2+b^2-b^2+2ab-2ab
=3a^2
=