Giải câu 2 trang 12 sách toán VNEN lớp 9 tập 2.
a) {x−2y=−87x+2y=−8
⇔{8x=−16x−2y=−8
⇔{x=−2x−2y=−8
⇔{x=−2y=3
b) {2x−5y=−1,15x−2y=0,1
⇔{20x−50y=−1150x−20y=1
⇔{100x−250y=−55100x−40y=2
⇔{210y=5750x−20y=1
⇔{y=1970x=970
c) {x3+y4=−112−3x+2y=−12
⇔{4x+3y=−1−3x+2y=−12
⇔{12x+9y=−3−12x+8y=−48
⇔{17y=−51−3x+2y=−12
⇔{y=−3−3x+2y=−12
⇔{x=2y=−3
d) {x+2y=555x+y=5+25
⇔{x+2y=5525x+2y=10+45
⇔{x+2y=55(25−1)x=−5+10
⇔{x=−5+1025−1x+2y=55
⇔{x=(−5+10)(25+1)19x+2y=55
⇔{x=19519x+2y=55
⇔{x=5y=25
