# Thread: hi there, can someone expand please?

1. ## hi there, can someone expand please?

hello again.

another equation which i am having some difficulty with:

two alternating currents I1 and I2 flow into a circuit node,the output current I is given by adding I1 and I 2.

find I and t, when I1 and I2 are as follows :

I1=5sin(50t +Pi/3)

I2=6cos50t.

so i can see from the 1st equation its obviously a compound angle formula i need to use. ie sin(a+b)=sina.sinb+cosa.cosb

so moving on i get sin50t x sin pi/3 + cos50t x cospi/3 which evetually comes out as 3.85t by my calculations ie I1 =3.85t?

i'm not sure really where to go with this or how to transform I2, it may be the cosine rule which is cosa.cosb +sina.sinb buts thats it i'm afraid my lesson book is not very clear either to be honest,so all in all toiling and getting uptight with this.

any hints appreciated

thanks in advance.

2. $I = I_1 + I_2 = 5\sin(50t + \frac{\pi}{3}) + 6\cos(50t)$

Numerical values of I and t cannot be found without a second equation relating I and t.

3. ## thanks

many thanks andrew where does it go from here though?