(define pi 3.14159265358979323846264338327950288419716939937510)

(define (triangle base height)
  (* .5 base height))

(define (heron a b c)
  (sqrt (* (/ (+ a b c) 2) (/ (- (+ a b) c) 2) (/ (- (+ a c) b) 2) (/ (- (+ b c) a) 2))))

(define (brahmagupta a b c d)
  (sqrt (* (/ (- (+ a b c) d) 2) (/ (- (+ a b d) c) 2) (/ (- (+ a c d) b) 2) (/ (- (+ b c d) a) 2))))

(define (convert3 a b c)
  (+ (* 100 c) (* 10 b) (* 1 a)))

(define (volume-cylinder r h)
  (* r r h pi))

(define (area-cylinder r h)
  (+ (* 2 pi r r) (* 2 pi r h)))

(define (volume-pipe r h t)
  (- (volume-cylinder r h) (volume-cylinder (+ r t) h)))

(define (area-pipe r h t)
  (- (+ (area-cylinder r h) (area-cylinder (+ r t) h) ) (* 4 pi r r)))

(define (rocket-height g t)
  (* (/ 1 2) g t t))