Several math problems in the first volume of the eighth grade

1, solution:

k=4/2=2

y=2x

AO^2=2^2+4^2=20

20-4^2=4

√4+2=4

B(4，0)

Let the analytical formula y = ax+b.

Substitute two-point coordinates

2a+b=4

4a+b=0

The solution is a=-2 b=8.

The analytical formula is y=-2a+8.

2、x？ +y？ +4x-6y+ 14

=(x+2)^2+(y-3)^2+ 1

Because (x+2) 2+(y-3) 2 > =0.

so(x+2)2+(y-3)2+ 1 >； = 1

So no matter what values x and y take, the algebraic expression x? +y？ The value of +4x-6y+ 14 is always positive.

3、(x^2+5x+5)^2

4、x？ -Really? +x-3y

=x^2-y^2+x-y-2y

=x^2-(y+ 1)^2+x-y+ 1

=(x-y- 1)(x+y+ 1)+x-y+ 1

5 、( x？ +2xy-3y？ )(x-y)

=(x+3y)(x-y)/(x-y)

=x+3y= 125

6、a(a- 1)-(a？ -b)=2

b-a=2

ab-(a？ +b？ )/2

=(2ab-a^2-b^2)/2

=-(a-b)^2/2=-(2^2)/2=-2