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#lang scheme
;; circlearea
;;
;; find the area of a circle with radius r
(define
(circlearea r)
(* 3.142 (expt r 2))
)
;; between?
;;
;; check whether a is between x and y
(define
(between? a x y)
(if
(or
(and (< y a) (> x a)) ;; y < a < x
(and (> y a) (< x a)) ;; x < a < y
)
#t
#f
)
)
;; shorter
;;
;; returns the list with fewer elements
(define
(shorter a b)
(if
(< (length a) (length b))
a
b
)
)
;; righttri?
;;
;; checks whether 3 integers can be the side lengths
;; of a right triangle.
(define
(righttri? a b c)
(cond
;; a is largest (b^2 + c^2 = a^2)
[ (and (> a b) (> a c)) (= (+ (expt b 2) (expt c 2)) (expt a 2)) ]
;; b is largest (a^2 + c^2 = b^2)
[ (and (> b a) (> b c)) (= (+ (expt a 2) (expt c 2)) (expt b 2)) ]
;; c is largest (a^2 + b^2 = c^2)
[ (and (> c a) (> c b)) (= (+ (expt a 2) (expt b 2)) (expt c 2)) ]
)
)
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