Evaluate
-\frac{\sqrt{2}}{2}\approx -0.707106781
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\cos(180+45)=\cos(180)\cos(45)-\sin(45)\sin(180)
Use \cos(x+y)=\cos(x)\cos(y)-\sin(y)\sin(x) where x=180 and y=45 to obtain the result.
-\cos(45)-\sin(45)\sin(180)
Get the value of \cos(180) from trigonometric values table.
-\frac{\sqrt{2}}{2}-\sin(45)\sin(180)
Get the value of \cos(45) from trigonometric values table.
-\frac{\sqrt{2}}{2}-\frac{\sqrt{2}}{2}\sin(180)
Get the value of \sin(45) from trigonometric values table.
-\frac{\sqrt{2}}{2}-\frac{\sqrt{2}}{2}\times 0
Get the value of \sin(180) from trigonometric values table.
-\frac{\sqrt{2}}{2}
Do the calculations.
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