Identify what property ( commutative identity distributive, or associative) is used.

a. y• 7 = 7y

b. 3y + (7+2y) = (3y +7) + 2y

c. y + 0 = y

d. 2 (x + 5 ) = 2x + 10

; _;

An angle that measures between 90 and 180° is called a(,

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.

For what values of the variable x is the expression square root of 7x+14+ square root of 7-x a real number?