       Re: extracting lhs or rhs of equations

• To: mathgroup at smc.vnet.net
• Subject: [mg16889] Re: [mg16853] extracting lhs or rhs of equations
• From: BobHanlon at aol.com
• Date: Mon, 5 Apr 1999 02:24:25 -0400
• Sender: owner-wri-mathgroup at wolfram.com

```In a message dated 4/2/99 4:24:32 AM, johnson at ae.msstate.edu writes:

>Let's say I have an expression like:
>
>  In:= eq1= Sin[x] == x;
>
>Is there a way to get just the left-hand side or right-hand side of the
>equation? Something like:
>
>  In:= LHS[eq1]
>  Out:= Sin[x]
>

David,

eq1= Sin[x] == x;

You can use Part to extract the LHS or RHS.

eq1[]

Sin[x]

First[eq1]

Sin[x]

eq1[]

x

Last[eq1]

x

For more complex expressions, you can use Part to extract any specific part

eqn2 = a*x^2 + b*x + c == 0;

eqn2[]

c + b*x + a*x^2

Table[eqn2[[1,k]], {k, 3}]

{c, b*x, a*x^2}

Table[eqn2[[1,3, k]], {k, 2}]

{a, x^2}

Table[eqn2[[1,3, 2, k]], {k, 2}]

{x, 2}

Bob Hanlon

```

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