( 1)2-4a？ +5a？ -6

=(5a？ -4a？ )+(2-6)

=a？ -4

2. Find the following values (reminder: merge similar projects first, and then evaluate them)

( 1)3c？ -8c+2c？ - 12c？ +2c-2c？ +1, where c=-2.

Original formula =(2c? -2c？ )+(3c？ - 12c？ )+(2c-8c)+ 1

=0-9c？ -6c+ 1

=-9c？ -6c+ 1

=-9×(-2)? -6×(-2)+ 1

=-36+ 12+ 1

=-23

(2)2)3y-6xy to the fourth power? The fourth power of -4y +7y? X, where x=-3 and y=2.

The fourth power of 3y -6xy? The fourth power of -4y +7y? x

= (the fourth power of = (the fourth power of 3y-4y) +(7y? x-6xy？ )

=-y to the fourth power +xy?

The fourth power of =-2 -3×2?

=- 16-24

=-40