[數學]代入消元法唔識做呀!!救命

1)y=2-3x=12-x^2y = 2 - 3x .......(1)
y = 12 - x^2 .....(2)代 (1) 入 (2) :2 - 3x = 12 - x^2x^2 - 3x - 10 = 0(x - 5)(x + 2) = 0x = 5 或 x = - 2當 x = 5 ,
y = 2 - 3(5) = - 13當 x = - 2 ,
y = 2 - 3(-2) = 8
2)2x-y=7.....(1)
x^2+y=8........(2)由(1) , y = 2x - 7 , 代入 (2) :x^2 + 2x - 7 = 8x^2 + 2x - 15 = 0(x - 3)(x + 5) = 0x = 3 或 x = - 5當 x = 3 ,
y = 2(3) - 7 = - 1當 x = - 5 ,
y = 2(-5) - 7 = - 17
3)
大明比小明大2歲，1年前大明的年齡等於小明的平方，求小明和大明現時的年齡。設小明現時的年齡 = x , 大明現時的年齡 = y :大明比小明大2歲 : x + 2 = y........(1)1年前大明的年齡等於小明的平方 : y - 1 = (x - 1)^2.......(2) (1) 代入 (2) :x+2 - 1 = (x - 1)^2x + 1 = x^2 - 2x + 1x^2 - 3x = 0x(x - 3) = 0x = 0 (不合理) 或 x = 3當 x = 3 , y = 3+2 = 5小明現時的年齡 = 3
大明現時的年齡 = 5

1)y=2-3x=12-x^2y = 2 - 3x .......(1)
y = 12 - x^2 .....(2)代 (1) 入 (2) :2 - 3x = 12 - x^2x^2 - 3x - 10 = 0(x - 5)(x + 2) = 0x = 5 或 x = - 2當 x = 5 ,
y = 2 - 3(5) = - 13當 x = - 2 ,
y = 2 - 3(-2) = 8
2)2x-y=7.....(1)
x^2+y=8........(2)由(1) , y = 2x - 7 , 代入 (2) :x^2 + 2x - 7 = 8x^2 + 2x - 15 = 0(x - 3)(x + 5) = 0x = 3 或 x = - 5當 x = 3 ,
y = 2(3) - 7 = - 1當 x = - 5 ,
y = 2(-5) - 7 = - 17
3)
大明比小明大2歲，1年前大明的年齡等於小明的平方，求小明和大明現時的年齡。設小明現時的年齡 = x , 大明現時的年齡 = y :大明比小明大2歲 : x + 2 = y........(1)1年前大明的年齡等於小明的平方 : y - 1 = (x - 1)^2.......(2) (1) 代入 (2) :x+2 - 1 = (x - 1)^2x + 1 = x^2 - 2x + 1x^2 - 3x = 0x(x - 3) = 0x = 0 (不合理) 或 x = 3當 x = 3 , y = 3+2 = 5小明現時的年齡 = 3
大明現時的年齡 = 5