>>Do you want the 42" output to mirror the 27", or do you need 3 separate monitor outputs?
>
>Laptop outputs HDMI to 27-inch monitor presently. That image would need to be replicated to a 42-inch monitor.
As Bill points out, a splitter should work in that case. The description for this product explains the difference between a splitter and a switch:
https://www.amazon.ca/Sewell-Direct-SW-23500-HDMI-Splitter/dp/B007WR0CHUIt seems if you have sophisticated needs you may need to pay attention to the level of HDMI support (1.3, 1.4 etc) and if/how HDCP is supported. You might want to look at product reviews at Amazon etc. I'm not knowledgeable about this.
Regards. Al
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