Me with it.
in the figure given below , ab and ac are two chords of a circle of center o and radius r. if ab= 2 ac and the perpendiculars drawn from the center on these chords are of lengths 'a' and 'b' respectively. prove that 4b^2= a^2+3r^2
this question is related to lesson circles

OK.  I did it.  Now let's see if I can go through it without
getting too complicated.

I think the key to the whole thing is this fact:

     A radius drawn perpendicular to a chord bisects the chord.

That tells us several things:

-- OM bisects AB. 
   'M' is the midpoint of AB.
   AM is half of AB.

-- ON bisects AC.
    'N' is the midpoint of AC.
   AN is half of AC.

--  Since AC is half of AB,
     AN is half of AM.
     a = b/2 

Now look at the right triangle inside the rectangle.
'r' is the hypotenuse, so

                                            a² + b² = r²

But  a = b/2, so             (b/2)² + b² = r²

(b/2)² = b²/4                   b²/4   + b² = r²

Multiply each side by 4:     b² + 4b² = 4r²
                                       -  -  -  -  -  -  -  -  -  -  -
                                            0  + 5b² = 4r²  
Repeat the
original equation:                a² +  b² =  r²

Subtract the last
two equations:                  -a² + 4b² = 3r² 

Add  a²  to each side:              4b²  =  a² + 3r² .    <=== ! ! !
 

, and

for

step-by-step explanation:

we can analyze the pattern at which the terms increase. let us denote , , , so that we can call

1 the 1st term, 3 the 2nd term, 6 the 3rd term,etc.

note the following:

from the 1st term (1) to the 2nd term (3), we go up by 2,from the 2nd term (3) to the 3rd term (6), we go up by 3from the 3rd term (6) to the 4th term (10), we go up by 4, andfrom the 4th term (10) to the 5th term (15), we go up by 5.

the pattern: to get the next term value, we just add the next term number (e.g. 1st, 2nd, to the previous term value (term values are the given numbers in the question, 1, 3, 6, 10, 15,

from , to get to , we add

from , to get to , we add

etc.

we need to form a recursive formula, a formula that has the next term as a function of the previous term. so a possible recursive formula can be

, and for