i cannot find all x values from abs(x) using solve() function

syms x

y=abs(x);

r=solve(y==1,x);

ans=

r = 1

but x can be 1 as well as -1,why doesnt they show -1 as well

Answer 1

[Steven Lord]

Tell solve to show you the parameterized solution and the conditions that those parameters need to satisfy in order for the parameterized solution to be valid.

syms x
y=abs(x);
r=solve(y==1,x, 'ReturnConditions', true)

r = struct with fields:
             x: exp(y*2i)
    parameters: y
    conditions: y <= pi & 0 <= y

x isn't the set [1, -1]. But that's because there are complex solutions.

yy = exp(1i/2) % This is r.x with parameter y = 1/4

yy = 0.8776 + 0.4794i

abs(yy)

ans = 1

Or if you only want real solutions tell solve that:

r=solve(y==1,x, 'ReturnConditions', true, 'Real', true)

r = struct with fields:
             x: [2×1 sym]
    parameters: [1×0 sym]
    conditions: [2×1 sym]

r.x

ans = 

[VISHNU PADMAKUMAR]

thank you soo much it works now