Please help asap!! Due today!

What is the number 321,000,000 in scientific notation? also what is the number? ?

Sundar used linear combination to solve the system of equations shown. he did so by multiplying the first equation by 5 and the second equation by another number to eliminate the y-terms. what number did sundar multiply the second equation by? 2x+9y=41 3x+5y=36

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).