tinhssssssssssssssssssssssssssssssssssssssssss

`C=sin^2 15^o + sin^2 35^o + sin^2 55^o + sin^2 75^o`

`=(sin^2 15^o + cos^2 15^o) + (sin^2 35^o + cos^2 35^o) `

`=1+1=2`

`D=cos^2 15^o + cos^2 35^o + cos^2 55^o + cos^2 75^o`

`=(cos^2 15^o + sin^2 15^o) + (cos^2 35^o + sin^2 35^o)`

`=1+1=2`

`\mathbb{C}=sin^2 15^@ + sin^2 35^@ + sin^2 55^@ + sin^2 75^@`

`= sin^2 15^@ + sin^2 35^@ + cos^2 (90^@-55^@)+cos^2 (90^@-75^@)`

`= sin^2 15^@ + sin^2 35^@ + cos^2 35^@ + cos^2 15^@`

`= (sin^2 15^@ + cos^2 15^@) + (sin^2 35^@ + cos^2 35^@)`

`=1+1=2`

`\mathbb{D}=cos^2 15^@ + cos^2 35^@ + cos^2 55^@ + cos^2 75^@`

`= cos^2 15^@ + cos^2 35^@ + sin^2 (90^@-55^@)+sin^2 (90^@-75^@)`

`= cos^2 15^@ + cos^2 35^@ + sin^2 35^@ + sin^2 15^@`

`= (cos^2 15^@ + sin^2 15^@) + (cos^2 35^@ + sin^2 35^@)`

`=1+1=2`

`@` Áp dụng công thức:

`sin^2 alpha + cos^2 alpha=1`