Question

已知不等式组。。。急要~~~

1.已知不等式组x>2a+a和x>a+2的解集是x>-1,求出a的取值。

Answer 1

x>3a
x>a+2
大大取大
则若3a>a+2
a>1时
是x>3a
所以3a=-1
a=-1/3,不符合x>1

若3a<=a+2
a<=1时
是x>a+2
所以a+2=-1
a=-3,符合x<=1

所以a=-3

Answer 2

①(X+1)(X+2)-(X+10)(X-7)
=X(X+2)+1*(X+2)-[X(X-7)+10(X-7)]
=X²+2X+X+2-(X²-7X+10X-70)
=X²+3X+2-X²-3X+70
=72

②5(X-1)(X+3)-2(X-2)(X-5)
=5(X²+3X-X-3)-2(X²-5X-2X+10)
=5X²+10X-15-2X²+14X-20
=3X²+24X-35

③(3-2a)(-2a-3)+(2a-6)(a+7)
=(-2a+3)(-2a-3)+(2a²+14a-6a-42)
=(-2a)²-3²+(2a²+8a-42)
=4a³-9+2a²+8a-42
=6a²+8a-51

④(3X²+2X-1)(X²-2X+4)-(3X^4-4X³)X
=(3X^4-6X³+24X²+2X³-4X²+8X-X²+2X-4)-(3X^5-4X^4)
=3X^4-4X³+19X²+10X-4-3X^5+4X^4
=-3X^5+7X^4-4X³+19X²+10X-4