數學功課,plz

1.-5(x-3)
=-5乘x + -5乘-3
=-5x15
=-75

2.(x+2)(x-9)
=x乘x + x乘-9 + 2乘x + 2乘-9
=x(2次)+ -9x + 2x + -18
=x(2次)+ -7x + -18

3.(y-2)^2
=2(y-2)
=2y-4

4.(5a+7)(6a-8)
=5a乘6a + 5a乘-8 + 7乘6a + 7乘-8
=30a + (-40a) + 42a + -56
=30a - 40a + 42a - 56
=32a -56

5.(8-3r)(r+5)
=8乘r + 8乘5 + (-3r)r + -3r乘5
=8r + 40 + -3r(2次) + -15r
=-7r + 40 -3r(2次)

1. -5(x-3) (將括號外的數字乘進括號內)

= -5x+15

2. (x+2)(x-9)

= x^2-9x+2x-18

= x^2-7x-18

3. (y-2)^2

= y^2+2(y)(2)-2^2

= y^2+4y-4

4. (5a+7)(6a-8)

= 30a^2-40a+42a-56

=30a^2+2a-56

5. (8-3r)(r+5)

=8r+40-3r^2-15r

= -3r^2-7r+40

answer與上述解答有所出入 請小心分辨

1.-5(X-3)
= -5 x X + (-5) x (-3)
= -5 x15
= -75

2.(X+2)(X-9)
=X x X + X x -9 + 2 x X + 2 x -9
=X^2 + (-9X) + 2X + (-18)
=X^2 -7x + -18

3.(y-2)^2
=y^2 +4y - 4

4.(5a + 7)(6a - 8)
=5a x 6a + 5a x (-8) + 7 x 6a + 7 x (-8)
=30a + (-40a) + 42a + (-56)
=30a - 40a + 42a - 56
=32a - 56

5.(8 - 3r)(r+5)
=8 x r + 8 x 5 + (-3r)r + (-3r) x 5
=8r + 40 + -3r^2 + (-15r)
= - 3r ^2 -7r + 40