Решите систему уравнений:
а) $left { {{ x^{2} +4xy+4y ^{2}=7x+14y } atop {2x+5y=15}} right.$
б) $. left { {{9y^{2}-6xy-5x+ x^{2}+15y=0 } atop {3x-4y=20}} right.$

$left { {{x^2+4xy+4y^2=7x+14y} atop {2x+5y=15}} right. left { {{(x+2y)^2=7(x+2y)} atop {2x+5y=15}} right. left { {{x+2y=7} atop {2x+5y=15}} right. left { {{x=7-2y} atop {2(7-2y)+5y=15}} right.$

$left { {{x=7-2y} atop {14-4y+5y=15}} right. left { {{x=7-2y} atop {14+y=15}} right. left { {{x=7-2y} atop {y=15-14}} right. left { {{x=7-2*1} atop {y=1}} right. left { {{y=5} atop {y=1}} right.$

$left { {{9y^2-6xy-5x+x^2+15y=0} atop {3x-4y=20}} right. left { {{9y^2-6xy+x^2=5x-15y} atop {3x-4y=20}} right. left { {{(3y-x)^2=-5(3y-x)} atop {3x-4y=20}} right.$

$left { {{3y-x=-5} atop {3x-4y=20}} right. left { {{-x=-5-3y} atop {3x-4y=20}} right. left { {{x=5+3y} atop {3x-4y=20}} right. left { {{x=5+3y} atop {3(5+3y)-4y=20}} right. left { {{x=5+3y} atop {15+9y-4y=20}} right.$

$left { {{x=5+3y} atop {5y=20-15}} right. left { {{x=5+3y} atop {5y=5}} right. left { {{x=5+3*1} atop {y=1}} right. left { {{x=8} atop {y=1}} right.$