4a+9b=70
4(3b + 7) + 9b = 70
12b + 28 + 9b = 70
21b = 70 - 28
21b = 42
b = 2
~~~~~~~~~~~~~~~~~~~~~~~~
a=3b+7
a = (3 * 2) + 7
a = 13
Using the substitution method, what is the value of a in the solution to the system of equations below?
a=3b+7
4a+9b=70
2 answers
a=3b+7...eq (1)
4a+9b=70 or 4a=-9b+70...eq (2)
multiplying equation i by 3
3(a)=3(3b+7)...eq (1)
3a=9b+21...eq (3)
subtracting equation (2) from eq(3)
4a=-9b+70...eq(2)
3a=9b+21...eq (3)
a = 49
this is the value of a
4a+9b=70 or 4a=-9b+70...eq (2)
multiplying equation i by 3
3(a)=3(3b+7)...eq (1)
3a=9b+21...eq (3)
subtracting equation (2) from eq(3)
4a=-9b+70...eq(2)
3a=9b+21...eq (3)
a = 49
this is the value of a
5 answers