angelinagarza43
contestada

what ia the value of cosθ given that (-2,9) is a point on the terminal side of θ ?

A.
[tex] - \frac{9 \sqrt{85} }{85} [/tex]
B.
[tex] -\frac{2 \sqrt{85} }{85} [/tex]
C.
[tex]\frac{9 \sqrt{85} }{85} [/tex]
D.
[tex]\frac{2 \sqrt{85} }{85} [/tex]

Respuesta :

Hello from MrBillDoesMath!



Answer:

Choice B,    -2  sqrt(85) / 85



Discussion:

By definition,

cos(@) =  length of side adjacent to angle / hypotenuse

            =  -2/ ( sqrt (    (-2)^2 + (9^2)   )              (usin Pythag. theorem)

            = -2/ sqty (4 + 81)

            = -2 / (sqrt(85)

Multiply numerator and denominator by sqrt(85):

           =  (-2 / ( sqrt(85) ) * (sqrt(85)/sqrt(85) )

           = -2  sqrt(85) / 85


which is choice B


Thank you,

MrB



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