如果6sinA + 8cosA = 10,如何证明TanA = 3/4?

如果6sinA + 8cosA = 10,如何证明TanA = 3/4?
Anonim

回答:

请参阅以下说明

说明:

#6sinA + 8cosA = 10#

将双方分开 #10#

#3 / 5sinA + 4 / 5cosA = 1#

#cosalpha = 3/5##sinalpha = 4/5#

#cosalpha = cosalpha / sinalpha =(3/5)/(4/5)= 3/4的#

因此,

#sinAcosalpha + sinalphacosA = SIN(A +阿尔法)= 1#

所以,

#A +阿尔法= pi / 2之间#, #mod 2PI#

#A = PI / 2-α#

#TANA = TAN(PI / 2-α)= cotalpha = 3/4的#

#TANA = 3/4的#

#QED#

回答:

见下文。

说明:

#或,6sinA - 10 = -8cosA#

#or,(6sinA -10)^ 2 =(-8cosA)^ 2#

#or,36sin ^ 2A- 2 * 6sinA * 10 + 100 = 64cos ^ 2A#

#or,36sin ^ 2A - 120sinA + 100 = 64cos ^ 2A#

#or,36sin ^ 2A - 120sinA + 100 = 64(1 - sin ^ 2A)#

#or,36sinA - 120sinA +100 = 64 - 64Sin ^ 2A#

#or,100 sin ^ 2A - 120SinA + 36 = 0#

#or,(10sinA-6)^ 2 = 0#

#or,10sinA - 6 = 0#

#or,SinA = 6/10#

#或,SinA = 3/5 = p / h#

使用毕达哥拉斯定理,我们得到

#b ^ 2 = h ^ 2 - p ^ 2#

#or,b ^ 2 = 5 ^ 2 - 3 ^ 2#

#or,b ^ 2 = 25 - 9#

#or,b ^ 2 = 16#

#or,b = 4#

#so,TanA = p / b = 3/4#

这个答案是否正确?

回答:

看解决方案

说明:

#6sinA + 8cosA = 10#

将双方分开 #sqrt(6 ^ 2 + 8 ^ 2)#=#10#

#(6sinA)/ 10 + 8cosA / 10 = 10/10 = 1#

#cosalphasinA + sinalphacosA#=1

哪里 #tanalpha = 4/3# 要么 #阿尔法= 53degree#

这转变为

#sin(阿尔法+ A)= sin90#

#alpha + A = 90#

#A = 90-α#

服用 ##晒黑双方

#TANA = TAN(90-α)#

#TANA = cotalpha#

#TANA = 3/4的#

#6sinA + 8cosA = 10#

#=> 3sinA + 4cosA = 5#

#=>(3/5)sinA +(4/5)cosA = 1#

#=>(3/5)sinA +(4/5)cosA =(sinA)^ 2 +(cosA)^ 2#

#color(red)(sin ^ 2A + cos ^ 2A = 1)#

#=>(3/5)sinA +(4/5)cosA = sinA * sinA + cosA * cosA#

#=> sinA = 3/5,cosA = 4/5#

因此, #tanA = sinA / cosA =(3/5)/(4/5)=(3/5)×(5/4)= 3/4#