Function or not a function?

Two times a number plus three times another number equals 4. three times the first number plus four times the other number is 7. find the numbers

Prove sin2a + cos2a - 1 / sin2a + cos2a + 1 = 1 - tana / 1 + cota

Afair die is cast four times. calculate the probability of obtaining exactly two 6's round to the nearest tenth of a percent