Đáp án:Bài 3:
1.\(\left \{ {{x=8} \atop {y=15}} \right.\)
2.\(\left \{ {{x=4} \atop {y=6}} \right.\)
3;\(\left \{ {{x=2} \atop {y=5}} \right.\)
4.\(\left \{ {{x=8} \atop {y=2}} \right.\)
Giải thích các bước giải:
Bài 3:
1.\(\left \{ {{\frac{3x}{4}+\frac{7y}{3}=41} \atop {\frac{5x}{2}-\frac{3y}{5}=11}} \right.\)
⇔\(\left \{ {{9x+28y=492} \atop {25x-6y=110}} \right.\)
⇔\(\left \{ {{225x+700y=12300} \atop {225x-54y=990}} \right.\)
⇔\(\left \{ {{754y=11310} \atop {25x-6y=110}} \right.\)
⇔\(\left \{ {{x=8} \atop {y=15}} \right.\)
2.\(\left \{ {{\frac{x}{y}=\frac{2}{3}} \atop {x+y-10=0}} \right.\)
⇔\(\left \{ {{3x-2y=0} \atop {x+y=10}} \right.\)
⇔\(\left \{ {{3x-2y=0} \atop {3x+3y=30}} \right.\)
⇔\(\left \{ {{-5y=-30} \atop {x+y=10}} \right.⇔\left \{ {{x=4} \atop {y=6}} \right.\)
3.\(\left \{ {{\frac{x+y}{3}+\frac{2}{3}=3} \atop {\frac{4x-y}{6}+\frac{x}{4}=1}} \right.\)
⇔\(\left \{ {{x+y+2=9} \atop {4(4x-y)+6x=24}} \right.⇔\left \{ {{x+y=7} \atop {22x-4y=24}} \right.\)
⇔\(\left \{ {{x=2} \atop {y=5}} \right.\)
4.\(\left \{ {{\frac{x+y}{3}=\frac{x-y}{5}} \atop {\frac{x}{4}=\frac{y}{2}+1}} \right.\)
⇔\(\left \{ {{3(x+y)=5(x-y)} \atop {x=2y+4}} \right.\)
⇔\(\left \{ {{2x-8y=0} \atop {x-2y=4}} \right.\)
⇔\(\left \{ {{2x-8y=0} \atop {2x-4y=8}} \right.\)
⇔\(\left \{ {{-4y=-8} \atop {x-2y=4}} \right.⇔\left \{ {{x=8} \atop {y=2}} \right.\)
