先化简,再求值.①(3x^2-xy)/(9x^2-6xy+y^2),其中x=4/3,y=-2/3②(2a-6b)/(a^2-9b^2),已知a+3b=-1/2

Question

先化简,再求值.
①(3x^2-xy)/(9x^2-6xy+y^2),其中x=4/3,y =-2/3
②(2a-6b)/(a^2-9b^2),已知a+3b=-1/2

Answer 1

1.3x^2-xy)/(9x^2-6xy+y^2)=X/(3X-Y)=2/7
2.(2a-6b)/(a^2-9b^2)=2/(a+3b）=-4