Math Is Fun Forum

numbergeek

Member

Registered: 2016-02-08

Posts: 4

Re: Trigonometry!

hi evene,

Q3.  That equation can be re-written with only cos.

Now use

So now the equation has only cos(A).  Subtract 1 from both sides so you can square to eliminate the square root sign.

Re-arrange and solve the quadratic.  You will find two values for cos(A).  One does not fit the original equation so can be discarded; the other does fit as you can easily show.

Bob

I'm working on this problem and having trouble with the last part--solving the quadratic. I'm ending up with a really strange looking quadratic, having to complete the square. Is that supposed to happen? Or am I making a silly math mistake that I'm just not catching? Thanks.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Trigonometry!

hi numbergeek

Hhmm.  That quadratic should work out easily.  Wonder what you're doing?

This factorises.  You can reject one factor as leading to a value that won't fit the original, leaving an answer that checks out.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

ET ag

Member

Registered: 2017-02-22

Posts: 10

Re: Trigonometry!

Wait...I still couldn't get an answer for the soccer ball problem, can you guy elaborate on your hints?

Thanks,
ET ag

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If a second was a minute, and a minute was an hour, how many hours would be in one day? (There are multiple answers and they are debatable)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Trigonometry!

hi ET ag

A soccer ball is constructed using 32 regular polygons with equal side lengths. Twelve of the polygons are pentagons, and the rest are hexagons. A seam is sewn wherever two edges meet. What is the number of seams in the soccer ball?

Number of hexagons = 32 - 12

Each hexagon has 6 sides and each pentagon has 5.  Before the ball is sewn together work out how many sides in total.  To make the ball pairs of sides are sewn together so halve this total.

If you post your working I'll check it over.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob