.....(1) We know that - √A2+B2≤A‌sinx+B‌cosx≤√A2+B2 Therefore,−√12+12≤sin‌x+cos‌x≤√12+12 ⇒−√2≤sin‌x+cos‌x Hence, we can say that the minimum value of sin‌x+cos‌x=−√2...(2) From equation (1) and (2) we can say that, ⇒3sin‌x+3cos‌x≥.2×3