The general equation of SHM is x=Asin‌ωt Which can be (in some condition) x=2Asin‌2ωt‌ or ‌A‌cos‌2‌ω‌t‌ etc. ‌ and the equation Asin‌ωt+B‌cos‌ω‌t may be represent the resultant of two SHM But Asin‌2ωt cannot show SHM.