Estimating with multiplying decimals estimate 2.7 times 4

To solve the system of equations below, pedro isolated the variable y in the first equation and then substituted it into the second equation. what was the resulting equation? { 5y=10x {x^2+y^2=36

Convert (-3,0) to polar form. a. (3,0’) b. (-3,180’) c. (3,180’) d. (3,360’)

Which has the greater energy, light of wavelength 519 nm or light with a frequency of 5.42 x 10^8 sec^-1?