Hello Venkatesh,
You can appear in KCET Exam but if you are failed in 10+2 then there there will be occur problem after exam during admission.
You can check here criteria for KCET
Candidate should have successfully passed the qualifying examination(10+2 or equivalent)

Candidate should have passed the qualifying examination with Physics and Mathematics as compulsory subjects and any one of the following as the additional subject  Chemistry/Biotechnology/Biology/Electronics/Computer. Should have also studied English.

Candidates waiting for their results of the qualifying exam in 2019 are also eligible to apply.

For more info you can visit to the given link
https://www.google.com/amp/s/engineering.careers360.com/articles/kcet-eligibility-criteria/amp.
Thank You.

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