SICP Exercise 1.3

Exercise 1.3.  Define a procedure that takes three numbers as arguments and returns the sum of the squares of the two larger numbers.

(define (ex3 x y z)
                     (cond
                       ((> y z x) ((define a x) (define b y) (+ (square a) (square b))))
                       ((> y x z) ((define a x) (define b y) (+ (square a) (square b))))
                       ((> z y x) ((define a x) (define b y) (+ (square a) (square b))))
                       ((> z x y) ((define a x) (define b y) (+ (square a) (square b))))
                       ((> x z y) ((define a x) (define b y) (+ (square a) (square b))))
                       ((> x y z) ((define a x) (define b y) (+ (square a) (square b)))))

I know I'm thinking about this the wrong way. My solution doesn't work.

This is very easy. You should've been able to figure this out yourself.

(define (square a) (* a a))
(define (sum-of-squares a b) (+ (square a) (square b)))
(define (ex3 x y z)
  (cond ((and (> y x) (> z x)) (sum-of-squares y z))
        ((and (> x y) (> z y)) (sum-of-squares x z))
        ((and (> x z) (> y z)) (sum-of-squares x y))))

It is simply a process of working out the smallest number, and then you know which two are the largest.