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

Maria heard on the radio that the high temperature that day would be to determine the temperature in degrees celsius, she used the formula , where c is the temperature in degrees celsius and f is the temperature in degrees fahrenheit.

Harry owes the bank money. to repay his debt, he paid $150 back to the bank each month. after 10 months, his remaining debt was $6900. what was the original amount of harry's debt? how long did it take harry to pay back his entire debt?