You should get tan a = 2/5, not tan a = -2/5. The addition formula of cos(A+B) includes the negative and thus you should get Rcos(a)=5 and Rsin(a)=2. I have included an image below to help you visualise the solution. As always, make sure to practice more of these questions. Hope this helps.
You should get tan a = 2/5, not tan a = -2/5. The addition formula of cos(A+B) includes the negative and thus you should get Rcos(a)=5 and Rsin(a)=2. I have included an image below to help you visualise the solution. As always, make sure to practice more of these questions. Hope this helps.
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