2(sin 15+ sin 75)^2

 

2(sin 15+ sin 75)^2  

 

I don't know how to combine trigonometric ratios to equivalencies. 

You can obtain the values from a table and then work out the arithmetic. 

 

I got                                          2 * (sin 15 + sin 75)²  

 

                                                 2 * (0.2588 + 0.9659)²  

 

                                                 2 * (1.2247)²  

 

                                                 2 * 1.4999  =  2.2497   

 

I did considerable rounding, though. You might want

to take those sine values out to more decimal places.  .

_.

Good rounding. I'm think that the expression winds up being 2*1.5=3.

I don't know why, but that is what I get.