Get a 2/30+b 2/ 10 = 1.

Let a=√30cost b=√ 10sint.

y=a+b=√30cost+√ 10sint

=2√ 10((√3/2) cost +( 1/2)sint)

=2√ 10sin(t+π/3)

a & gt0，b & gt0

2kπ