simulraneous equations -2

M

meano

New member
Joined
Oct 27, 2014
Messages
37
Subhotosh, can you help with this simultaneous equation? I need to find s & t. I have worked out t to be 4.5. I thought I had correctly worked out s to be -3.9 but when verifying equation 2 it didn't work out.

The equations are

5s + 3t + 6 = 0

3s + 5t + 18 = 0

If you could point me in the right direction I'll try and work it out correctly from there. Thanks
 
I have tried multiplying the equations to make the s coefficient equal. Then deducting equation 2 from 1 works out t to be -1.5.

I then use this to work out s which is -0.3. This does not solve the equation correctly. I am struggling here and i sure the solution is staring at me in the face but I can't see it.
 
meano said:
I have tried multiplying the equations to make the s coefficient equal. Then deducting equation 2 from 1 works out t to be -1.5.

I then use this to work out s which is -0.3. This does not solve the equation correctly. I am struggling here and i sure the solution is staring at me in the face but I can't see it.
Click to expand...
O.K., to follow what you did: Start with
5s + 3t + 6 = 0
3s + 5t + 18 = 0.
Multiply the first equation by 3 and the second equation by 5 to make the s coefficients equal
15s + 9t + 18 = 0
15s + 25t + 90 = 0
Deduct equation 2 from equation 1
0 s - 16 t - 72 = 0
or
t = - 72/16 = -4.5
Since your answer was -1.5, it looks like you made a mistake in doing this (I'm pretty sure I didn't but one never knows).
 
meano said:
Subhotosh, can you help with this simultaneous equation? I need to find s & t. I have worked out t to be 4.5. I thought I had correctly worked out s to be -3.9 but when verifying equation 2 it didn't work out.

The equations are

5s + 3t + 6 = 0

3s + 5t + 18 = 0

If you could point me in the right direction I'll try and work it out correctly from there. Thanks
Click to expand...

15s + 9t + 18 = 0 .........................(1)

15s + 25t + 90 = 0 ........................(2)

subtract (1) from (2)

16t + 72 = 0 → t = - 9/2

Using the value of 't' in (1)

15 s + 9*(-9/2) + 18 = 0 → 15 s - 45/2 = 0 → s = 3/2

using the values of 's' and 't' in (2), we get,

15s + 25t + 90 = 15*(3/2) + 25*(-9/2) + 90 = 0 → (45-225)/2 + 90 → (-180/2) + 90 = 0 CHECKS....

 
I sorted it guys thanks. I wasn't multiplying the whole equation, I only multiplied the s coefficients. I must be tired. Thanks for all the replies.
 
Yeah I know, I did say the solution was staring right at me and I was right. Lesson learnt!
 
You must log in or register to reply here.
Top