ok this is in an example in a first-year physics textbook, yet some how i spent an hour trying to solve it (identities, tricks, etc) and could not find a solution.(adsbygoogle = window.adsbygoogle || []).push({});

here is what the textbook states:

(1) v2f*cos[tex]\phi[/tex] = 3.5*10^5 - v1f*cos(37)

(2) v2f*cos[tex]\phi[/tex] = v1f*sin(37)

"now we sqaure these two equations and add them"

= 1.23*10^11 - 7*10^5*v1f*cos(37) + v1f^2*cos(37)^2 + v1f^2*sin(37)^2

(then it simplifies further)

I know that 1.23*10^11 is (3.5*10^5)^2 and that 7*10^5 is 2*3.5*10^5

any help in explaining how this equation is derived would be a great help (ESPECIALLY how 7*10^5 seems to pop out of no where)

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# Simple algerba

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