x = arctan(-2/7)+pin ~~ 0.2783 + pinx=arctan(−27)+πn≈0.2783+πn
Explanation:
2cos(x)+7sin(x)=02cos(x)+7sin(x)=0
=> 7sin(x)=-2cos(x)⇒7sin(x)=−2cos(x)
=> sin(x)/cos(x) = -2/7⇒sin(x)cos(x)=−27
=> tan(x) = -2/7⇒tan(x)=−27
=> x = arctan(-2/7)+pin, n in ZZ
~~0.2783+pin
Note that we add npi to account for tan(x) being periodic with a period of pi, thus tan(arctan(-2/7)) = tan(arctan(-2/7)+pi)=tan(arctan(-2/7)+2pi) = ...