Help solving these please...... :-) ?

Question

The profit on a watch is given by P=x^2 - 5x - 9 and where x is the number of watches sold per day. How many watches were sold on a day when there was a 15.00 loss?

--I think I set it up this way... x^2 - 5x - 9= -15 , but then I am lost?? Is that right? It doesn't factor. Should it??

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The number of people infected after t days is P=200 + 5t - t^2. Find the number of days until the number of people infected is 150.

Same with this one. Wouldn't it be set up this way?

-t^2+5t+200=150

Thanks in advance!!!!

Answer 1

I rarely use factors in quadratic problems. I think the using the formula is way better

Answer 2

x^2-5x-9=-15

add -15

x^2-5x+6=0

factor

(x-2)(x-3)=0

x=2, 3

-t^2+5t+200=150

-t^2+5t+50=0

t^2-5t-50=0

(t-10)(t+5)=0

t=10 days

Answer 3

you have them both rihght

Answer 4

You set up your problems correctly.  Just do the algebra next.