Re: simple equation substitutions

*To*: mathgroup at smc.vnet.net*Subject*: [mg128547] Re: simple equation substitutions*From*: Bob Hanlon <hanlonr357 at gmail.com>*Date*: Fri, 2 Nov 2012 00:45:26 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <20121101071928.99D326857@smc.vnet.net>

eqns = {y == x + 2, x == 7}; Solve[eqns, {x, y}] {{x -> 7, y -> 9}} Solve[eqns, Variables[eqns]] {{x -> 7, y -> 9}} Simplify[Solve[eqns[[1]], y], eqns[[2]]] {{y -> 9}} Simplify[Solve[#[[1]], y], #[[2]]] &@eqns {{y -> 9}} Solve[eqns, y, Integers] {{y -> ConditionalExpression[9, x == 7]}} Reduce[eqns, {x, y}] // ToRules {x -> 7, y -> 9} Reduce[eqns, y] // ToRules {x -> 7, y -> 9} Reduce[eqns, x] // ToRules {y -> 9, x -> 7} Eliminate[eqns, x] // ToRules {y -> 9} Bob Hanlon On Thu, Nov 1, 2012 at 3:19 AM, Neal Becker <ndbecker2 at gmail.com> wrote: > {y == x + 2, x == 7} > > Solve[%, y] > > -> {} > > What I expected to happen is have x->7 applied to y == x+2. > > My real plan is to develop a list of (a lot more complicated) expressions that will have repeated substitutions applied. > > Why didn't the above work and/or what should I do instead? >

**References**:**[newb] simple equation substitutions***From:*Neal Becker <ndbecker2@gmail.com>