英文數學題

1(a)
a + 3b = 18
--> a = 18 - 3b
sub a = 18 - 3b into 3a + 5b = 34*****************
get: 3 * (18 - 3b) + 5b = 34
54 - 9b + 5b = 34
4b = 20
b = 5 //
so, a = 18 - 3*(5) = 18 - 15 = 3 //

(b) 16w = 5 - 4s
--> 8w = 2.5 - 2s
sub 8w = 2.5 - 2s into 3s - 8 = 8w + 7
get: 3s - 8 = 2.5 - 2s + 7
5s = 17.5
s = 3.5 //
and 8w = 2.5 - 2*(3.5) = -4.5
so w = -0.5625 (or -9/16) //


2(a) 5x - 2y = 6 ---(1)
3x + 2y = 10 ---(2)
(1)+(2): 5x + 3x = 6 + 10
8x = 16
x = 2 //
sub x = 2 into (2)
3*(2) + 2y = 10
6 + 2y = 10
2y = 4
y = 2 //

1a. a+3b=18-------1
3a+5b=34-----2
From 1,
a=18-3b--------3
Substitute 3 into 2
3(18-3b)+5b=34
54-9b+5b=34
-4b=-20
b=5------4
Substitute 4 into 3
a=18-3(5)
a=18-15
a=3
so a=3,b=5

1) a=18-3b
sub. a=18-3b
3(18-3b)+5b=34
54-9b+5b=34
-9b+5b=34-54
-4b=-20
b=5
sub. b=5
a=18-3(5)
a=3
Ans : a=3 & b=5