Fibonacci Sequences

[Yendall]

Hello everyone!
I am little puzzled by this problem that I overcame in the textbook.
I understand Fibonacci Sequences and can solves problems like this for example:

Name the terms represented by:
i) t27 + t28
Obviously this would equal t29.
Those types of problems I understand.

However, this one stumped me, and i'm sure there is a simple way of solving it, the textbook just never explained it.

It is:
t11 + 2xt12 + t13

How do I deal with the 2xt12?

Thanks for any help you guys can provide!

Max.

EDIT: nevermind I understand this now:

t11 = 89
2xt12 = 288
t13 = 233

89 + 288 + 233 = 610
t15= 610
thus
t11+2t12+t13 = t15

[plato]

A more general method is
    t11 + 2xt12 + t13
=  (t11 + t12) + (t12 + t13)
=  t13  +  t14
=  t15

[Yendall]

A more general method is
    t11 + 2xt12 + t13
=  (t11 + t12) + (t12 + t13)
=  t13  +  t14
=  t15

oh i see how it would work like that, thank you! that would save much more time.