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Show that `|{:("sin"10^(@), -"cos"10^(@)), ("sin"80^(@), "cos"80^(@)):}| =1.` |
Answer» We have `|{:("sin"10^(@), -"cos"10^(@)), ("sin"80^(@), "cos"80^(@)):}|` `=("sin"10^(@))("cos" 80^(@)) - ("sin" 80^(@))(-"cos" 10^(@))` `= ("sin" 10^(@) "cos" 80^(@) + "cos" 10^(@) "sin"80^(@))` `= "sin" (10^(@) +80^(@)) " "[because "sin" A"cos" B + "cos" A"sin" B = "sin (A+B)]` `="sin" 90^(@) =1.` |
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