What is x and y ???!

The multiplication property of zero states that the product of any number and 0 is 0. what must be true about either a or b to make ab=0

You are on a cycling trip around europe with friends. you check the weather forecast for the first week. these are the temperatures for the week. sun mon tues wed thurs fri sat 16°c 20°c 24°c 28°c 28°c 23°c 15°c what is the mean temperature forecast for the week?

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.