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3. Evaluare \( \cos 75 \cos 45-\cos 15 \cos 45 \) cos \( 79 \sin 311+\sin 101 \sin 49 \) 3.2 Determine the value of \( \sin 3 x \cos y+\cos 3 x \sin y \) 3.3 Dftermine the value of \( x^{2}+y^{2} \) if \( x=2 \cos \theta\{y=2 \)

Ask by Knight Nunez. in South Africa
Feb 28,2025

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Calculate the following expressions: 1. \( \cos(75) \cos(45) - \cos(15) \cos(45) \) 2. \( \cos(79) \sin(311) + \sin(101) \sin(49) \) 3. \( \sin(3x) \cos(y) + \cos(3x) \sin(y) \) 4. \( x^{2} + y^{2} \) where \( x = 2\cos(\theta) \) and \( y = 2 \) Solutions: 1. \( \cos(75) \cos(45) - \cos(15) \cos(45) = \frac{\cos(120) - \cos(60)}{2} \) 2. \( \cos(79) \sin(311) + \sin(101) \sin(49) = -0.446954 \) 3. \( \sin(3x) \cos(y) + \cos(3x) \sin(y) = \sin(3x + y) \) 4. \( x^{2} + y^{2} = (2\cos(\theta))^{2} + 2^{2} = 4\cos^{2}(\theta) + 4 \)

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Beyond the Answer

O metodă simplă de a evalua \( \cos 75 \cos 45 - \cos 15 \cos 45 \) este să extragi factorul comun \( \cos 45 \) din expresie. Așadar, avem \(\cos 45 (\cos 75 - \cos 15)\). Folosind formula pentru diferența cosinusurilor, putem obține o expresie simplificată. În plus, se știe că \(\cos 45 = \frac{\sqrt{2}}{2}\), ceea ce face calculul mult mai ușor! Pentru \( \sin 3x \cos y + \cos 3x \sin y \), recunoaștem că acesta este formatul pentru suma sinusurilor. Așadar, putem rescrie expresia ca \( \sin(3x + y) \). Acesta este un pas util în simplificarea problemelor trigonometrice și îți permite să evaluezi mai ușor expresia prin substituirea valorilor corespunzătoare pentru \(x\) și \(y\).

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