# Equation problem.

1. Jan 20, 2014

### brenfox

1. The problem statement, all variables and given/known data

Determine the power generated by a voltage V = 240∠15° volts driving a current I = 12 ∠75°

2. Relevant equations

P=VIcos(ø-ø)

3. The attempt at a solution This is a worked example from my open university course. The answer is 240x12cos(15°-75°) = 1440W. I can not for the life in me work out how they have arrived at this answer. I get cos-60= 0.58. then times 240x12= 1692.9 W. Must be doing something wrong!

2. Jan 20, 2014

### Staff: Mentor

How is cos(60°) equal to 0.58?

3. Jan 20, 2014

### pasmith

It is possible that the OP has their calculator in GRAD mode, since cos(60 grad) = 0.588.

But really one shouldn't need a calculator to calculate cos(60°) = 0.5.

4. Jan 20, 2014

### brenfox

Not sure. After inputting cos 60 it came out with 0.58. I am of the understanding cosine 60 equals half. so 240x12x0.5 does equal 1440 Watts . But cosine 60 equates to 0.58 in my calculator.

5. Jan 20, 2014

### Staff: Mentor

As pasmith indicated, check to make sure that your calculator is in degree mode for angles, not grad mode.