解下3道选择题
2个回答
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(5)
(2,0)
ax-by=18
2a=18
a=9
(4,9)
4a-9b=18
36-9b=18
9b=18
b=2
a+3b=9+6=15
ans : D
(6)
(1,-2)
ax+by=-48
a-2b=-48 (1)
2ax+5y=90
2a-10=90
a=50 (2)
from (1)
50-2b=-48
b=49
a^2-b^2 = 50^2-49^2=99
ans :B
(7)
|x+y-2|+(2x+y+4)^2=0
x+y-2=0 (1)
2x+y+4=0 (2)
(2)-(1)
x=-2
from (1)
-2+y-2=0
y=4
ans : B
(2,0)
ax-by=18
2a=18
a=9
(4,9)
4a-9b=18
36-9b=18
9b=18
b=2
a+3b=9+6=15
ans : D
(6)
(1,-2)
ax+by=-48
a-2b=-48 (1)
2ax+5y=90
2a-10=90
a=50 (2)
from (1)
50-2b=-48
b=49
a^2-b^2 = 50^2-49^2=99
ans :B
(7)
|x+y-2|+(2x+y+4)^2=0
x+y-2=0 (1)
2x+y+4=0 (2)
(2)-(1)
x=-2
from (1)
-2+y-2=0
y=4
ans : B
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