If neither a nor b are equal to zero, which answer most accurately describes the product of (a + bi)(a - bi)?

the imaginary part is zero.
the real part is zero.
the imaginary part is positive.
the real part is not positive.

The swimming pool is open when the high temperature is higher than 20∘c. lainey tried to swim on monday and thursday (which was 3 days later). the pool was open on monday, but it was closed on thursday. the high temperature was 30∘c on monday, but decreased at a constant rate in the next 3 days. write an inequality to determine the rate of temperature decrease in degrees celsius per day, d, from monday to thursday.