若多项式a²-a+2的值为7,则多项式-1/5a²+1/5a-3的值为____________.

若多项式a²-a+2的值为7,则多项式-1/5a²+1/5a-3的值为____________.
若多项式a²-a+2的值为7,则多项式-1/5a²+1/5a-3的值为____________.

若多项式a²-a+2的值为7,则多项式-1/5a²+1/5a-3的值为____________.
a²-a+2的值为7
∴a²-a=5
-1/5a²+1/5a-3
=-1/5(a²-a)-3
=-1/5×5-3
=-4