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F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?

Jada has a meal in a restaurant she adds up the prices listed on the menu for everything they ordered and gets a subtotal of $42.00. when the check comes, it says they also need to pay $3.99 in sales tax. what percentage of the subtotal is the sales tax

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