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a) sin 40 - cos 50 =0
b) sin230 + sin240 + sin250 + sin260 = 2
c) cos210 - cos220 + cos230 - cos240 - cos250 - cos270 + cos280 = - sin230
\(a.sin40^o-cos50^o=sin40^o-sin40^o=0\)
\(b.sin^230^o+sin^240^o+sin^250^o+sin^260^o=\left(sin^230^0+sin^260^o\right)+\left(sin^240^0+sin^250^o\right)=\left(sin^230^0+cos^230^o\right)+\left(sin^240+cos^240^o\right)=1+1=2\)
\(c.\left(cos^210^o+cos^280^o\right)-\left(cos^220^o+cos^270^0\right)-\left(cos^240^o-cos^250^o\right)+cos^230^o=\left(cos^210^o+sin^210^o\right)-\left(cos^220^o+sin^220^o\right)-\left(cos^240^o+sin^240^0\right)+cos^230^0=1-1-1+\dfrac{3}{4}=-\dfrac{1}{4}\)
a, cos220o + cos240o + cos250o + cos270o
= (cos220o + cos270o) + (cos240o + cos250o)
= (cos220o + sin220o) + (cos240o + sin240o)
= 1 + 1 = 2
Mình nghĩ chắc sin285o là sin255o
b, sin225o + sin245o + sin265o + sin255o
= (sin225o + sin265o) + (sin245o + sin255o)
= (sin225o + cos225o) + (sin245o + cos245o)
= 1 + 1 = 2
Chúc bn học tốt!
a: \(=\left(\cos^215^0+\cos^275^0\right)+\left(\cos^225^0+\cos^265^0\right)+\left(\cos^235^0+\cos^255^0\right)+\cos^245^0\)
=1+1+1+1/2
=3,5
b: \(=\left(\sin^210^0+\sin^280^0\right)-\left(\sin^220^0+\sin^270^0\right)+\left(\sin^230^0\right)-\left(\sin^240^0+\sin^250^0\right)\)
=1-1-1+1/4
=-1+1/4=-3/4
c: \(=\left(\sin15^0-\cos75^0\right)+\left(\sin75^0-\cos15^0\right)+\sin30^0\)
=1/2
a) Vì 20 ° < 70 ° n ê n sin 20 ° < sin 70 ° (góc tăng, sin tăng)
b) Vì 25 ° < 63 ° 15 ' n ê n cos 25 ° > cos 63 ° 15 ' (góc tăng, cos giảm)
c) Vì 73 ° 20 ' > 45 ° n ê n t g 73 ° 20 ' > t g 45 ° (góc tăng, tg tăng)
d) Vì 2 ° < 37 ° 40 ' n ê n c o t g 2 ° > c o t g 37 ° 40 ' (góc tăng, cotg giảm )
a: \(=\left(sin^210^0+sin^280^0\right)+\left(sin^220^0+sin^270^0\right)+sin^245^0\)
\(=1+1+\dfrac{1}{2}=\dfrac{5}{2}\)
b: \(=\left(sin^242^0+sin^248^0\right)+\left(sin^243^0+sin^247^0\right)+...+sin^245^0\)
=1+1+1+1/2
=3,5
c: \(=tan35^0\cdot tan55^0\cdot tan40^0\cdot tan50^0\cdot tan45^0=1\)
d: \(=\left(cos^215^0+cos^275^0\right)-\left(cos^225^0+cos^265^0\right)+\left(cos^235^0+cos^255^0\right)-\dfrac{1}{2}\)
=1-1+1-1/2
=1/2