How do you solve the simultaneous equations 4x+5y=0 and 8x-15y=5?

1 Answer
Apr 11, 2018

x=0.25 and y=-0.2

Explanation:

For simultaneous equations you have to know 2 rules:
• Same signs subtract
meaning if both equations have the same sign you subtract to cancel out x or y

•Different signs add
meaning if both equations have different signs you add to also cancel out x or y

In this case, you will add both equations because they are of different signs

4x + 5y = 0
8x-15y=5

multiply the first equation by 3 to cancel out y values by adding

after multiplying you'll have
12x+15y=0
+
8x-15y=5
now add both equations
20x=5
x=5/20
x=0.25

Substitute the value of x in either of the equations

4x+5y=0
4(0.25)+5y=0
1+5y=0
5y=-1
y=-1/5 or -0.2

so x=0.25 and y=-0.2