2x＋7y＝9①
x－4y＝3②
①-②×2
7y+8y=9-6
y=1/5
代y=1/5入②
x-4×1/5=3
x=19/5
∴x+y=19/5+1/5=4若實數(shù)x,y滿足x＋y＝4,x²y＋xy²＝－8,則｜x－y｜的值為？x²y＋xy²＝－8
即：xy(x+y)=-8
∵x＋y＝4

∴xy=-2
∴｜x－y｜=√(x-y)²
=√[(x+y)²-4xy]
=√[4²-4×(-2)]
=√(16+8)
=√24
=2√6